This invention relates to a method and apparatus for cold starting an engine, and more particularly, to a method and apparatus for enhancing the cold starting capability of a spark ignition, internal combustion engine, which is fueled with an alcohol-based fuel mixture.
In the past, alcohol fuels, such as ethanol and methanol, have been proposed as possible alternatives to gasoline for fueling conventional internal combustion engines. It is well known that engines using these alternative fuels generally can not be started at low ambient temperatures, due to the higher heats of vaporization, lower vapor pressures, and the higher fuel concentrations required to achieve stoichiometric fuel-air mixtures for alcohol fuels.
To successfully cold start a spark ignition engine, a sufficient amount of fuel must be vaporized to provide a combustible fuel vapor-air mixture in the vicinity of each engine spark plug. However, attempts to achieve a combustible fuel vapor-air mixture by increasing the flow of an alcohol fuel during cold starting have been unsuccessful, due to the occurrence of repeated engine misfires.
Various approaches have been heretofore suggested for improving the cold starting capability of alcohol fueled engines, including the use of fuel preheaters to assist fuel vaporization and additional fuel injectors for injecting fuel in two-stages to increase the flammability of cylinder fuel vapor-air mixtures. Although these approaches have shown some success, they require that conventional engines be augmented with complex and costly fuel preheaters or auxiliary fuel injection systems.
It is also known that a small quantity of gasoline can be mixed with methanol or ethanol to increase the fuel vapor pressure, and thereby improve engine cold-starting and warm-up operation. One example of an alcohol-based fuel that is gaining popularity as a commercially feasible automobile fuel is commonly known as M-85. This fuel is formed by mixing 15% gasoline with 85% methanol. Testing has shown that conventional engines generally can not be started at ambient temperatures below -20.degree. C. with the M-85 fuel, which is still significantly higher than a desired minimum cold starting temperature of -29.degree. C., that is a commonly used standard for automobiles.
Consequently, there exists a need for a convenient method and apparatus for improving the cold starting performance of a spark ignition, internal combustion engine at low ambient temperatures, when the engine is fueled with an alcohol-based fuel mixture.